AC12: Spectroscopic analysis
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When molecules absorb infrared radiation, what does the absorbed energy do the the bond
Make the covalent bonds in the molecule vibrate
Fragments in a mass spectrometer must carry a ________ charge
Positive
What does NMR stand for
Nuclear Magnetic Resonance
In proton NMR, what are the units of the chemical shift
ppm
In proton NMR, what is the area under the peak proportional to
The number of protons that contribute to it
When the NMR peaks split, what do the number of splits mean
How many protons are attached to the neighbouring carbons
If there were 2 protons on an adjacent carbon, how many peaks would there be in the NMR peak
3 peaks
What is the name for 2 peaks after splitting in an NMR spectrum
A doublet
If there’s 3 protons on adjacent carbon, how many peaks will there be after splitting
4 peaks
If the peak in the NMR splits into 3, what is this called
Triplet
If the peak in an NMR splits into 4, what is this called
Quartet
What is the equation/ rule for the number of peaks the peak splits into
n+1
In the n+1 rule, what does the n stand for
The number of protons on adjacent carbon
What are the 2 exceptions of the n+1 rule
• OH peaks are never split and the -OH protons don’t cause splitting of adjacent protons • Equivalent protons don’t split each other
When doing a proton NMR, what must the solvent not contain
Hydrogen
Why can’t the solvent for a proton NMR machine contain hydrogen
Since the machine would pick up the protons present in the solvent and produce extra peaks
What type of solvent is used in proton NMR
Deuterated solvents
What is deuterium
An isotope of hydrogen
What is the formula for a deuterated solvent that is very similar to water
D2O
When is the D2O shake useful
To detect NH or OH peaks in molecule
How does the D2O shake work
By exchanging the proton on the OH or NH with deuterium, D, which isn’t detected on the NMR
Draw propan-1-ol, how many peaks will there be in the carbon-13 NMR
3
Draw propan-2-ol, how many peaks will there be in the carbon-13 NMR
2 peaks
What happens in proton NMR but not carbon-13 NMR
Splitting